I'm generally in agreement here, I think that manifold is hurting your torque without a significant HP payback up top.

A performer RPM will certainly help your upper bottom and probably work the converter harder throughout the middle, I just don't know if I would prefer it over a mildly ported Street Dominator on your 383 which I think will be just as strong through the middle and (at least from my personal experience) a bit better up top.

The Best thing about a BB Mopar is it's so easy to swap the intakes and compare them literally back to back at the track.